Lachish was a city overlooking the hills west of Jerusalem. It needed to be captured before attacking Jerusalem.
The aqueduct that supplies water to the upper pool was on the north side of Jerusalem, not the Gihon Spring in the Kidron Valley.
Isaiah met Ahaz on this road leading to the field where cloth is washed about 33 years earlier (see Isaiah 7:3). At that time, he urged Ahaz to trust God. However, Ahaz trusted Assyria instead, leading to this desperate situation. Now, the challenge to trust God came from mocking foreign voices (see Isaiah 28:11–13).